1. Field of the Invention
This invention relates to improvements to an apparatus used in semiconductor deposition operations and, more particularly, to an improved means for providing a closure for apertures formed in the walls of such an apparatus.
2. Description of the Prior Art
During the manufacture of semiconductors it is necessary to form layers of depositions on a semiconductor wafer. This would typically be done in a deposition chamber of a processing apparatus, the operation of which is illustrated with reference to FIG. 1 of the accompanying drawings.
In a typical processing apparatus a number of silicon wafers 10 are stacked in a wafer rack 12. Individual wafers 14 are sequentially removed from the rack by means of a robot arm 16 and inserted into a particular chamber 18 through an open aperture or slit 19.
In this figure, four independent chambers 18, 18.1, 18.2 and 18.3 are shown. Each chamber has its own slit, 19, 19.1, 19.2 and 19.3, associated with it and the robot arm 16 services all four chambers. Once the wafer 14 has been inserted into the chamber, the aperture 19 is closed by a mechanism generally referred to as a slit valve closure mechanism 20. For the sake of clarity only one closure mechanism is illustrated, however, in practice a separate closure mechanism exists for each slit 19, 19.1, 19.2 and 19.3. After the slit 19 is closed, the deposition process commences. Once the deposition has been completed, the closure mechanism 20 is operated to open the slit 19 and the wafer is removed from the chamber 18 by the robot arm 16 and inserted into another processing chamber 18.1 or returned to the rack 12.
One prior art slit valve closure mechanism 20 is illustrated in FIG. 2. In this figure a closure 22 for the slit or aperture 19 in the sidewall 34 of a chamber is held in place in a first, sealing position by means of an arm 24 carrying a roller 30 which bears against a wedge-shaped block 26. It is usual to have two identical arm and roller combinations in each slit valve closure mechanism, but, as their operation is identical, only one is described below.
The arm 24 is rotationally mounted on a shaft 28 so as to be rotatable from the sealing position shown to an open position clear of the aperture 19 as indicated by broken lines 24'. During this rotation the closure 22 pivots about a shaft 21 from the sealing position into the open position. Shaft 21 is journalled to suitable brackets (not shown) extending outwardly from sidewall 34. The motive force required to move the arm 24 between these two positions is provided by a piston and cylinder actuator which will be later described with reference to FIG. 3.
As the arm 24 moves in the counter-clockwise direction (in this figure) to lift the closure 22 to close the aperture 19, the roller 30 at the end of the arm 24 bears against the wedge-shaped portion 32 of the block 26. Further counter-clockwise movement of the arm 24 causes the roller 30 to move up the wedge-shaped portion 32 in the direction of increasing thickness across the wedge. This in turn forces the closure 22 to bear with increasing force against the sidewall 34 of the furnace. It has been determined that the combined force of the two rollers 30 onto the wedge-shaped block 26 can exceed 500 pounds (2.3 kN). The closure 22 seals against the sidewall 34 as a result of a circumferential O-ring 38 mounted in a groove in the closure 22.
During the opening procedure, the arm 24 moves in the clockwise direction and a spring 36 comes into play to break the seal of the closure 22 over the aperture 19 and move the closure 22 away and into its open position.
Now, it is known in the semiconductor manufacturing industry that during a deposition procedure it is essential that contamination of the interior atmosphere of the chamber is reduced to an absolute minimum as such contamination would be detrimental to deposition and related procedures.
Unfortunately, the prior art device described above has the disadvantage that its operation generates particles which tend to contaminate the interior of the furnace. This is because as the roller 30 bears on the wedge-shaped block 26, the large bearing force causes the surface of the wedge-shaped portion 32 to flake. This flaking is exacerbated by the repetitive process of opening and closing of the aperture 20 as wafers are inserted and removed.
Sometimes, when the closure 22 is closed, the O-ring 38 sticks to the sidewall 34. This prevents the spring 36 from releasing the closure 22, from the sidewall 34, in time for the robot arm to pass through.
The effect of these is that the closure 22 interferes with the operation of the robot arm and may possibly destroy the wafer or damage the arm.
A further problem with the prior art device is that it is very difficult to align the two arms (one of which is not shown) to bring equal force to bear on the closure 22. This is particularly so after the device has completed many cycles of opening and closing and the resultant wearing of the mechanism has caused misalignment.
The need therefore has arisen for a means for closing an aperture in a deposition chamber or the like, which can be repeatedly opened and closed without leading to the contamination of the interior of the furnace, which can readily be realigned and readjusted, and which, will provide reliable, repetitive opening and closure of the aperture. Furthermore, if needed, an improved means for closing should preferably be retrofitable to existing valve closure mechanisms with a minimum amount of rework.